1. Field of the Invention
The present invention generally relates to telecommunication systems and, more particularly, to a portable, two-part electronic data acquisition and storage system used in the field to facilitate alignment and realignment of telecommunications equipment.
2. Description of the Prior Art
In a point-to-multipoint telecommunication system such as a CATV system, there are many tree configuration circuits, inclusive of trunk and branch parts each containing multiple amplifiers. Such systems are complex to install and maintain due to the fact that there are many active circuits which can effect the overall performance of the system. Moreover, the coaxial cables generally employed in these systems are lossey, subject to temperature variations and must be properly terminated to avoid standing waves, all of which have a contributing effect on the performance of individual amplifiers in the system.
The initial installation of the system requires that each amplifier in the system be tuned to achieve system balance. Thereafter, it is necessary to routinely check each amplifier in the field and retune where necessary to maintain system balance. When an amplifier fails, the installation of a replacement amplifier requires that this amplifier be tuned to again achieve system balance.
More particularly, the goal of a CATV system is to deliver to customers the same signal level for, say, channel 2 as for channel 13; however, this type of signal delivery is not possible over the entire frequency spectrum of the system and, therefore, tuning is a matter of optimizing performance over the cable bandwidth for each individual amplifier. While a number of contaminants accumulate to impair visual acuity of delivered pictures, there are primarily two limiting factors which must be considered in the design and maintenance of amplifiers in a CATV system. If too much output level is demanded, cumulative third order intermodulation distortion becomes excessive on any given channel. On the other hand, if amplifier gain is too low, the signal level for some channels will be too low for succeeding amplifiers resulting in increased channel noise levels.
Both carrier-to-intermodulation and carrier-to-noise ratios can be observed by a spectrum analyzer. The intermodulation test is for beat frequencies caused by three frequencies, thus producing third-order distortion. Systems with high channel counts continuously battle to control the cumulative third order intermodulation or composite triple beat. Also, the nonlinearity portion of the amplifier's transfer function produces crossmodulation and composite triple beats and also causes intermodulation distortion. Use of the spectrum analyzer to locate and measure these beats, which are located close to video carriers, is a simple task in that the spectrum analyzer is simply connected to the system at sufficient signal level. Likewise, in order to measure carrier-to-noise ratio, the spectrum analyzer can be connected at almost any system test point, provided that there is enough system signal level. Essentially, a test carrier that has no other carrier on either side of it is needed. The carrier is selected by the analyzer center frequency control and the span adjusted to cover this one channel and the adjacent vacant channel. Once the carrier has been measured, the center frequency is adjusted to avoid sideband energy and the video filter contained in the spectrum analyzer is placed in the 300 Hz position. The noise is averaged by the filter, thus raising the baseline in the vacant carrier area. Reading the noise measurement to where the raised baseline intersects the screen graticule and comparing this result with the previously determined carrier amplitude provides a measure of the carrier-to-noise (C/N) ratio.
While these test procedures are in themselves relatively simple to make in a laboratory, they must be made in the field for each of the amplifiers in the system on original installation and periodically thereafter to maintain the system in optimum condition.